four-year-old和middle-aged 杠表示是什么?

问题描述:

four-year-old和middle-aged 杠表示是什么?

用横杠连接表示把组合词变成只能修饰名词的定语,其中复数名词要改为单数.例:four years old(a boy is four years old) 变形后作定语a four-year-old boy.